US4081714A - Method of coating the inner wall of a low-pressure mercury vapor discharge lamp with luminescent material - Google Patents

Method of coating the inner wall of a low-pressure mercury vapor discharge lamp with luminescent material Download PDF

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Publication number
US4081714A
US4081714A US05/732,472 US73247276A US4081714A US 4081714 A US4081714 A US 4081714A US 73247276 A US73247276 A US 73247276A US 4081714 A US4081714 A US 4081714A
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United States
Prior art keywords
wall
luminescent material
weight
envelope
pressure mercury
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Expired - Lifetime
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US05/732,472
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Anthonius Clemens Mossel
Joannes Petrus Hertogh
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US Philips Corp
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US Philips Corp
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/02—Use of particular materials as binders, particle coatings or suspension media therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/38—Devices for influencing the colour or wavelength of the light
    • H01J61/42—Devices for influencing the colour or wavelength of the light by transforming the wavelength of the light by luminescence
    • H01J61/46—Devices characterised by the binder or other non-luminescent constituent of the luminescent material, e.g. for obtaining desired pouring or drying properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
    • H01J9/20—Manufacture of screens on or from which an image or pattern is formed, picked up, converted or stored; Applying coatings to the vessel
    • H01J9/22—Applying luminescent coatings
    • H01J9/221—Applying luminescent coatings in continuous layers
    • H01J9/225—Applying luminescent coatings in continuous layers by electrostatic or electrophoretic processes

Definitions

  • the invention relates to a method of coating the inner wall of a low-pressure mercury vapour discharge lamp with luminescent material in which finely dispersed luminescent material is introduced into the lamp envelope by means of a gas stream.
  • the luminescent material is conveyed by means of an electric field and adheres to the wall of the lamp envelope.
  • U.S. Pat. No. 2,426,016 proposes to apply the luminescent material to the inner wall of a low-pressure mercury vapour discharge lamp by means of an electric field.
  • Such a method is also used to coat the inner wall of the outer envelope of a high-pressure mercury vapour discharge lamp.
  • it is customary to add a small quantity of silicon dioxide to the luminescent material to improve the adhesion.
  • silicon dioxide is used in the coating material of low-pressure mercury vapour discharge lamps this oxide absorbs mercury during operation of the lamp which causes a pronounced decrease in the light output of such lamps.
  • a method according to the invention is characterized in that prior to introducing the luminescent material into the envelope a quantity of 0.01% by weight to 1.0% by weight of stearic acid and/or palmetic acid and/or their salts, as well as a quantity of 0.1% by weight to 3.0% by weight of a nitrate is added.
  • This method has the advantage that the particles of the luminescent material are highly charged and that the applied coating absorbs mercury only to a slight degree.
  • a further advantage of adding the above mentioned acids and/or salts to the luminescent material is that not only charging the particles proceeds satisfactorily but also that the adhesion to the wall is optimum.
  • a quantity of 0.01% by weight to 1.0% by weight of calcium stearate is added to the luminescent material.
  • this material the charge distribution over the luminescent material is particularly uniform. Furthermore, the charge which is applied to the particles is then so large that expulsion of the charged particles which are still in motion, by those which have already settled to the wall of the lamp envelope is avoided.
  • a quantity of 0.1% by weight to 3.0% by weight of strontium or calcium nitrate is added to the stearic acid and/or palmetic acid and/or to the salts thereof.
  • strontium or calcium nitrates results in a very good adhesion of the luminescent material to the wall. Also the stacking of the granules is very favourable which results in a very uniform layer.
  • One of the means by which the luminescent material may be introduced into the envelope of the lamp is a spray gun having a voltage of, for example 25 kilovolts with respect to the wall, which is preferably grounded and from which gun the luminescent powder is sprayed into the envelope together with the charging and adhesion media. In the generated electric field the charged particles move to the wall of the lamp envelope.
  • a special embodiment of a method according to the invention there is added to the luminescent material besides stearic acid and/or palmetic acid and/or one or more salts thereof also between 0.05% by weight and 0.5% by weight of finely dispersed aluminium oxide having an average particle size smaller than 0.1 ⁇ m.
  • aluminium oxide in the above-mentioned procedure has the advantage that the granular particles of the luminescent material do not form aggreates when transported through the spray pipe. In addition it appears that this aluminium oxide positively influences the adhesion of the particles to the wall without being detrimental to the light output.
  • a quantity of 0.25 grams of calcium stearate (Ca (C 18 H 35 O 2 ) 2 , melting point ⁇ 180° C) and 1.25 gram of calcium nitrate (Ca(No 3 ) 2 , melting point ⁇ 560° C) is added to a suspension of 500 grams of luminescent material, for example antimony- and manganese-activated calcium halophosphate (Ca 10 (PO 4 ) 6 F 1 .7 Cl 0 .3) in 140 ml of ethanol.
  • the composite suspension was stirred for approximately 5 minutes and was then evaporated to dryness at a temperature of approximately 125° C.
  • a quantity of 0.5 grams of finely dispersed aluminium oxide having an average particle size smaller than 0.1 ⁇ m is added after the evaporation to dryness.
  • the powder mixture obtained in this way may now be introduced into the lamp envelope by means of an apparatus which is diagrammatically shown in the FIGURE.
  • reference 1 indicates a tubular glass envelope to be coated.
  • This lamp envelope is located between two holders 2 and 3 and rotates during the coating procedure.
  • the powder mixture which must be brought into the lamp envelope is contained in a powder vessel 4 which, in order to avoid aggregation of the powder is heated to a temperature of approximately 80° C, for example by means of an electric heating coil 5.
  • the powder is drawn into the spray pipe 8 by means of an injector 7, while compressed air the carrier gas is admitted at conduit 6.
  • a water-filled wash bottle 9 is placed in the spray pipe for moistening the air (the carrier gas) in order to improve the adhesion of the powder to the wall 1.
  • the spray pipe is connected to a glass tube, the end of which is provided with a nozzle 10, which can move in the longitudinal direction with respect to the lamp envelope.
  • the nozzle 10 is provided with a narrow slit-like opening 11. During passage the granules of the luminescent material are electrostatically charged by friction.
  • the nozzle is also provided with a so-called antenna 12 to which a high voltage, for example 25 kV with respect to the wall 1 is applied.
  • the wall of the lamp envelope which is heated to a temperature of 200° C by means of a heating element 14 is preferably grounded.
  • the granules which are electrostatically charged by means of friction move under the influence of the electric field which has been produced by the difference in voltage between the antenna and the wall, to the part of the wall located opposite the antenna.
  • the entire inner wall of the lamp envelope is provided owing to a uniform movement of the nozzle from the holder 3 to the holder 2 with a uniform layer of luminescent material.
  • the air escapes again from the lamp envelope.
  • it takes approximately 15 seconds to coat the entire envelope of a tubular lamp intended for a low-pressure mercury vapour discharge lamp having an output of 40W, a diameter of 36 mm and a length of 1200 mm.
  • the warm lamp envelope cools to approximately 25° C whereafter the tube is flushed with super-heated steam of ⁇ 200° C for approximately 20 seconds. This process considerably improves the adhesion of the luminescent material to the lamp envelope.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Vessels And Coating Films For Discharge Lamps (AREA)
  • Luminescent Compositions (AREA)
  • Formation Of Various Coating Films On Cathode Ray Tubes And Lamps (AREA)

Abstract

A method of electrostatic coating the inner wall of a low-pressure mercury vapour discharge lamp with luminescent material. Stearic acid and/or palmetic acid and/or salts thereof are added to the luminescent material together with nitrate in order to obtain a proper adhesion of the luminescent powder to the wall of the lamp.

Description

The invention relates to a method of coating the inner wall of a low-pressure mercury vapour discharge lamp with luminescent material in which finely dispersed luminescent material is introduced into the lamp envelope by means of a gas stream. The luminescent material is conveyed by means of an electric field and adheres to the wall of the lamp envelope.
In the production of low-pressure mercury vapour discharge lamps it is customary to deposit a coating of luminescent material on the inner wall of a usually tubular lamp envelope by spraying a suspension of the luminescent material in a medium which contains a binder, for example nitrocellulose and an appropriate solvent, for example butylacetate into the lamp envelope. A disadvantage of this method is that the use of the suspension necessitates long drying periods. In addition, relatively large quantities of luminescent material are wasted owing to dripping. Furthermore, the luminescent coat is usually not very uniform which is detrimental to the light output of the lamps and produces an inferior appearance.
To avoid the above drawbacks, U.S. Pat. No. 2,426,016 proposes to apply the luminescent material to the inner wall of a low-pressure mercury vapour discharge lamp by means of an electric field.
Such a method is also used to coat the inner wall of the outer envelope of a high-pressure mercury vapour discharge lamp. In that method it is customary to add a small quantity of silicon dioxide to the luminescent material to improve the adhesion. When silicon dioxide is used in the coating material of low-pressure mercury vapour discharge lamps this oxide absorbs mercury during operation of the lamp which causes a pronounced decrease in the light output of such lamps.
A method according to the invention is characterized in that prior to introducing the luminescent material into the envelope a quantity of 0.01% by weight to 1.0% by weight of stearic acid and/or palmetic acid and/or their salts, as well as a quantity of 0.1% by weight to 3.0% by weight of a nitrate is added.
This method has the advantage that the particles of the luminescent material are highly charged and that the applied coating absorbs mercury only to a slight degree. A further advantage of adding the above mentioned acids and/or salts to the luminescent material is that not only charging the particles proceeds satisfactorily but also that the adhesion to the wall is optimum.
In a particular embodiment of the method according to the invention a quantity of 0.01% by weight to 1.0% by weight of calcium stearate is added to the luminescent material. When this material is used the charge distribution over the luminescent material is particularly uniform. Furthermore, the charge which is applied to the particles is then so large that expulsion of the charged particles which are still in motion, by those which have already settled to the wall of the lamp envelope is avoided.
By preference, in accordance with the invention a quantity of 0.1% by weight to 3.0% by weight of strontium or calcium nitrate is added to the stearic acid and/or palmetic acid and/or to the salts thereof. In combination with stearic and/or palmetic acids and/or salts thereof the use of these nitrates results in a very good adhesion of the luminescent material to the wall. Also the stacking of the granules is very favourable which results in a very uniform layer.
One of the means by which the luminescent material may be introduced into the envelope of the lamp is a spray gun having a voltage of, for example 25 kilovolts with respect to the wall, which is preferably grounded and from which gun the luminescent powder is sprayed into the envelope together with the charging and adhesion media. In the generated electric field the charged particles move to the wall of the lamp envelope.
In a special embodiment of a method according to the invention there is added to the luminescent material besides stearic acid and/or palmetic acid and/or one or more salts thereof also between 0.05% by weight and 0.5% by weight of finely dispersed aluminium oxide having an average particle size smaller than 0.1 μm. The use of aluminium oxide in the above-mentioned procedure has the advantage that the granular particles of the luminescent material do not form aggreates when transported through the spray pipe. In addition it appears that this aluminium oxide positively influences the adhesion of the particles to the wall without being detrimental to the light output.
The invention will now be further explained with reference to an example for preparing a mixture which is introduced into the lamp envelope.
Preparing the mixture to be used
A quantity of 0.25 grams of calcium stearate (Ca (C18 H35 O2)2, melting point ± 180° C) and 1.25 gram of calcium nitrate (Ca(No3)2, melting point ± 560° C) is added to a suspension of 500 grams of luminescent material, for example antimony- and manganese-activated calcium halophosphate (Ca10 (PO4)6 F1.7 Cl0.3) in 140 ml of ethanol. The composite suspension was stirred for approximately 5 minutes and was then evaporated to dryness at a temperature of approximately 125° C. To prevent the calcium halophosphate particles from aggregating during subsequent processing, a quantity of 0.5 grams of finely dispersed aluminium oxide having an average particle size smaller than 0.1 μm is added after the evaporation to dryness.
The powder mixture obtained in this way may now be introduced into the lamp envelope by means of an apparatus which is diagrammatically shown in the FIGURE.
In the FIGURE reference 1 indicates a tubular glass envelope to be coated. This lamp envelope is located between two holders 2 and 3 and rotates during the coating procedure. The powder mixture which must be brought into the lamp envelope is contained in a powder vessel 4 which, in order to avoid aggregation of the powder is heated to a temperature of approximately 80° C, for example by means of an electric heating coil 5. The powder is drawn into the spray pipe 8 by means of an injector 7, while compressed air the carrier gas is admitted at conduit 6. Before the injector 7 a water-filled wash bottle 9 is placed in the spray pipe for moistening the air (the carrier gas) in order to improve the adhesion of the powder to the wall 1. The spray pipe is connected to a glass tube, the end of which is provided with a nozzle 10, which can move in the longitudinal direction with respect to the lamp envelope. The nozzle 10 is provided with a narrow slit-like opening 11. During passage the granules of the luminescent material are electrostatically charged by friction. The nozzle is also provided with a so-called antenna 12 to which a high voltage, for example 25 kV with respect to the wall 1 is applied. The wall of the lamp envelope which is heated to a temperature of 200° C by means of a heating element 14 is preferably grounded. After leaving the opening 11 in the nozzle the granules which are electrostatically charged by means of friction move under the influence of the electric field which has been produced by the difference in voltage between the antenna and the wall, to the part of the wall located opposite the antenna. The entire inner wall of the lamp envelope is provided owing to a uniform movement of the nozzle from the holder 3 to the holder 2 with a uniform layer of luminescent material. At 13 the air escapes again from the lamp envelope. In one embodiment of the method in accordance with the invention it takes approximately 15 seconds to coat the entire envelope of a tubular lamp intended for a low-pressure mercury vapour discharge lamp having an output of 40W, a diameter of 36 mm and a length of 1200 mm. Immediately after coating the warm lamp envelope cools to approximately 25° C whereafter the tube is flushed with super-heated steam of ± 200° C for approximately 20 seconds. This process considerably improves the adhesion of the luminescent material to the lamp envelope.

Claims (5)

What is claimed is:
1. A method of coating the inner wall of the envelope of a low-pressure mercury vapour discharge lamp with luminescent material which comprises: providing a suspension of luminescent material, introducing into said suspension a quantity of 0.01% by weight to 1.0% by weight of a material selected from the group consisting of stearic acid, palmetic acid, and salts thereof, in addition to a quantity of 0.1% by weight to 3.0% by weight of a nitrate, introducing said suspension into the lamp envelope by means of a gas stream, and conveying said suspension by means of an electric field to the wall of the lamp envelope.
2. A method as claimed in claim 1, characterized in that a quantity selected from said group is entirely calcium stearate.
3. A method as claimed in claim 1 wherein said nitrate is selected from the group consisting of strontium and calcium nitrate.
4. A method as claimed in claim 1 further including the step of adding before said step of introducing said suspension into said envelope of adding 0.05 and 0.5% by weight of finely dispersed aluminium oxide having an average grain size smaller than 0.1 micron.
5. A low-pressure mercury vapour discharge lamp having a lamp envelope having the inner wall coated with a luminescent layer manufactured in accordance with a method as claimed in claim 1.
US05/732,472 1975-10-17 1976-10-14 Method of coating the inner wall of a low-pressure mercury vapor discharge lamp with luminescent material Expired - Lifetime US4081714A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL7512190 1975-10-17
NLAANVRAGE7512190,A NL179956C (en) 1975-10-17 1975-10-17 METHOD FOR COVERING THE INNER WALL OF A LOW-PRESSURE MERCURY DISCHARGE LAMP WITH LUMINESCENT MATERIAL

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US4081714A true US4081714A (en) 1978-03-28

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JP (1) JPS5251780A (en)
CA (1) CA1088814A (en)
DE (1) DE2646610C2 (en)
FR (1) FR2328277A1 (en)
GB (1) GB1505628A (en)
NL (1) NL179956C (en)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4158071A (en) * 1977-09-09 1979-06-12 The Continental Group, Inc. Method and apparatus for power coating of three-piece cans
US4393100A (en) * 1979-12-26 1983-07-12 General Electric Company Method of coating a fused silica envelope
US4597984A (en) * 1985-06-03 1986-07-01 General Electric Company Method and apparatus for coating fluorescent lamp tubes
US4914723A (en) * 1983-03-08 1990-04-03 Thorn Emi Plc Fluorescent lamp discharge tube having electrostatically coated envelope
US4948530A (en) * 1988-09-26 1990-08-14 Patent-Treuhand-Gesellschaft Fur Elektrische Gluhlampen M.B.H. Method to make a reflective coating on high-pressure discharge lamps
US5314723A (en) * 1992-06-09 1994-05-24 Gte Products Corporation Method of coating phosphors on fluorescent lamp glass
EP0605250A3 (en) * 1992-12-29 1994-12-28 Flowil Int Lighting Coating lamp glass with phosphor.
US6265821B1 (en) * 1993-02-23 2001-07-24 Rockwell Collins, Inc. Serpentine avionics fluorescent tube with uniformity of luminance and chromaticity
KR20030071142A (en) * 2002-02-27 2003-09-03 박채문 a painting method of a light's glass cover
US20050037151A1 (en) * 2001-03-06 2005-02-17 Nordson Corporation Method and apparatus for powder coating hollow objects

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
HU202333B (en) * 1989-02-24 1991-02-28 Tungsram Reszvenytarsasag Low-pressure mercury vapour discharge source of light in first of all electric discharge lamp with a luminescent layer having inactive ingredient and a luminescent composition for mercury vapour discharge source of light

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2478387A (en) * 1944-06-10 1949-08-09 Eastman Kodak Co Phosphorescent materials
US2749251A (en) * 1953-10-29 1956-06-05 Tracerlab Inc Source of luminosity
US2854413A (en) * 1953-08-13 1958-09-30 Du Pont Phosphors
US2940864A (en) * 1954-03-24 1960-06-14 Sylvania Electric Prod Method of preparing a fluorescent screen
US3947608A (en) * 1973-11-26 1976-03-30 U. S. Philips Corporation Method of manufacturing an electrically conducting layer on an internal wall part of a cathode-ray tube

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE450318A (en) *
DE881549C (en) * 1941-11-29 1953-07-02 Westinghouse Electric Corp Process for producing a coating in a glass or similar vessel by the action of an electrostatic high-voltage field on introduced dry powder
FR1107826A (en) * 1953-09-25 1956-01-05 Sylvania Electric Prod Advanced fluorescent lamp
US2878137A (en) * 1956-03-30 1959-03-17 Sylvania Electric Prod Method of coating electric lamp envelopes
DE1177269B (en) * 1959-10-05 1964-09-03 Pintsch Licht G M B H Process for making powdery phosphors flowable

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2478387A (en) * 1944-06-10 1949-08-09 Eastman Kodak Co Phosphorescent materials
US2854413A (en) * 1953-08-13 1958-09-30 Du Pont Phosphors
US2749251A (en) * 1953-10-29 1956-06-05 Tracerlab Inc Source of luminosity
US2940864A (en) * 1954-03-24 1960-06-14 Sylvania Electric Prod Method of preparing a fluorescent screen
US3947608A (en) * 1973-11-26 1976-03-30 U. S. Philips Corporation Method of manufacturing an electrically conducting layer on an internal wall part of a cathode-ray tube

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4158071A (en) * 1977-09-09 1979-06-12 The Continental Group, Inc. Method and apparatus for power coating of three-piece cans
US4393100A (en) * 1979-12-26 1983-07-12 General Electric Company Method of coating a fused silica envelope
US4914723A (en) * 1983-03-08 1990-04-03 Thorn Emi Plc Fluorescent lamp discharge tube having electrostatically coated envelope
US4597984A (en) * 1985-06-03 1986-07-01 General Electric Company Method and apparatus for coating fluorescent lamp tubes
US4948530A (en) * 1988-09-26 1990-08-14 Patent-Treuhand-Gesellschaft Fur Elektrische Gluhlampen M.B.H. Method to make a reflective coating on high-pressure discharge lamps
US5314723A (en) * 1992-06-09 1994-05-24 Gte Products Corporation Method of coating phosphors on fluorescent lamp glass
US5441774A (en) * 1992-06-09 1995-08-15 Osram Sylvania Inc. Method of coating phosphors of fluorescent lamp glass
EP0605250A3 (en) * 1992-12-29 1994-12-28 Flowil Int Lighting Coating lamp glass with phosphor.
US6265821B1 (en) * 1993-02-23 2001-07-24 Rockwell Collins, Inc. Serpentine avionics fluorescent tube with uniformity of luminance and chromaticity
US20050037151A1 (en) * 2001-03-06 2005-02-17 Nordson Corporation Method and apparatus for powder coating hollow objects
KR20030071142A (en) * 2002-02-27 2003-09-03 박채문 a painting method of a light's glass cover

Also Published As

Publication number Publication date
GB1505628A (en) 1978-03-30
JPS5251780A (en) 1977-04-25
FR2328277A1 (en) 1977-05-13
NL179956C (en) 1986-12-01
DE2646610C2 (en) 1984-05-30
FR2328277B1 (en) 1981-08-28
NL7512190A (en) 1977-04-19
NL179956B (en) 1986-07-01
CA1088814A (en) 1980-11-04
DE2646610A1 (en) 1977-04-28
JPS5746615B2 (en) 1982-10-04

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